The invention relates to the sealing of a bared section of the wall of a hollow body made of a composite based on a thermoplastic and reinforcing fibres, for example glass fibres.
The invention will be more particularly described in the case of hollow bodies of the type such as pipes intended to convey pressurized fluids. However, it is not limited to this application and may, for example, relate to pressurized tanks containing pressurized fluids.
To convey pressurized fluids, it is known to use pipes made of a reinforced thermoplastic, which pipes have the advantage, while being just as strong, of being lighter than pipes made of cast iron or cement, or even pipes made only of thermoplastic.
This type of pipe, like that described in French Patent Application FR 98/13293 consists of a matrix made of a thermoplastic, for example polyethylene, a matrix-encapsulating layer based on reinforcing fibres advantageously mixed into a thermoplastic identical to that of the matrix, and a thermoplastic coating covering the encapsulating layer and preferably identical to the material of the matrix.
Two pipes of the aforementioned type are joined together by means of joining devices which necessarily have a sealing system for sealing the end faces of the pipes to be butted together.
French Patent Applications FR 2728051 and FR 00/00073 disclose joining devices for which a seal intended to be firmly applied against the facing end faces of the two pipes is provided.
However, in this case the sealing of the end face of a pipe is achieved only when making a joint. Now, before making such a joint, the pipes after manufacture may remain stored without any sealing protection being applied to them and are this liable to be attacked by external agents.
In the situation in which the bared end faces of a pipe have not been protected and are exposed to high compressive forces by water or by a fluid, the pressurized water or fluid may, over time, seep into the encapsulating layer along the reinforcing fibres. This may cause internal failure of the thermoplastic, possibly resulting in blisters visible on the external surface of the pipe; the mechanical strength of the pipe can therefore no longer be guaranteed.
We described above the problem of sealing the bared end faces of a pipe, but the same problem arises when a cut is made through the wall of the pipe for the purpose, for example, of tapping off another pipe.
Moreover, as a precaution, it may be desirable even if a sealed connection has to be made at the end face of a pipe or of any cut, to seal the internal material of which the pipe is composed, particularly the reinforcing fibres which in no case must come into contact with the fluid conveyed, in order to avoid any risk of contamination and to satisfy food criteria.
An object of the invention is therefore to seal the free openings of a hollow body based on a thermoplastic and reinforcing fibres, or any cut in the wall which bares the internal composition of which the hollow body is composed.
According to the invention, several alternative ways of implementing the method for producing the seal may be envisaged depending on the dimensions of the cross-section and its location in the hollow body.
The method for sealing a bared section in the wall of a hollow body based on a thermoplastic and on reinforcing fibres, the hollow body being especially intended for conveying or containing a pressurized fluid, the surface and the contours of the section being coated with a protective thermoplastic which is heated while it is being deposited and is compatible with the said thermoplastic of the hollow body in order to achieve complete adhesion, is characterized in that the protective thermoplastic is deposited in the form of an approximately flat bead of material which is largely melted using a heat gun.
According to another way of implementation, the method is characterized in that the protective thermoplastic is, for the purpose of depositing it, in the form of a piece which perfectly matches its surface and its contours. This piece may be deposited using a heating tool capable of sitting over the surface and the external edge of the section, such as an annular bell, which makes it possible to bring about a reduction in the diameter of the section.
According to yet another way of implementing the method, the protective thermoplastic consists of the external coating made of a thermoplastic of a second hollow body partly intended to be housed in the said section when the main hollow body has to be tapped off by means of the second hollow body.
According to one characteristic, the section is preheated before the protective plastic is deposited.
According to another characteristic, pressure is exerted on the surface and the contours of the section during or after deposition of the protective thermoplastic. The protective thermoplastic will be deflashed after it has cooled, so as to make the sealed section neat.
The method of the invention may especially be applied to a hollow body which advantageously consists of a matrix made of a thermoplastic, an encapsulating layer made of a thermoplastic in which glass fibres are mixed, and a coating made of a thermoplastic, the thermoplastic of the matrix preferably being identical to those of the encapsulating layer and the coating, and to the protective thermoplastic.